As the use of marine containers or other cargo container which are internally lined with bags, becomes more common for the transportation of dry flowable bulk products, as an alternative to the transportation in bulk vessels, the number and types of bulk products being transported in such marine containers is also growing. These bulk type products now include chemicals, minerals, agricultural and many other varied bulk products.
Such a variety of bulk products need to be matched with an appropriate bulk packaging format able not only to contain the product inside of the marine container for transportation, but also facilitate its loading and unloading. Container liner-bags fulfill that task, as they are flexible bags made of plastic laminated woven or film material, typically polyethylene, that once hung inside of the container, they occupy the full cargo volume inside of the marine or other type container, and they allow for the loading, transportation and unloading of any dry flowable bulk product.
Therefore, the design of the marine and other container liner-bag will vary depending on the methodology or equipment used by the shipper to load its bulk product into the marine or other containers, and the methodology or equipment used by the receiver of the bulk cargo to unload it from the marine or other containers.
Another crucial factor in the design of a marine or other container liner-bags will be the material characteristics of the bulk product itself which includes density, bulk density, angle of repose, hygroscopicity, physical aspect, temperature, and other physical attributes of the bulk product. All these physical characteristics determine how easy or difficult it is for the product to be handled when loading or unloading. Dry bulk products that are easy to handle flow easily into and out of the container liner-bag. Examples of easy to flow products are plastic resins in pellet form, dry whole grains and in general any material of grain or pellet nature. Dry bulk products that are difficult to handle flow poorly. Examples of hard to flow products are cement, titanium dioxide, starches and in general most powder type products.
In general, product compaction is a big problem and it is typically a function of the angle of repose of the bulk product, the attrition and rheology of its particles, humidity absorption tendency, and the degree of settling of the product inside of the liner-bag over the transportation journey.
These hard-to-flow bulk products in particular pose a real challenge to their transportation in marine container liner-bags when it is time to unload these bulk products. Their handling is especially difficult due to their very poor flow properties and the inherent settling over time during transportation. This difficulty results in the product compacting inside of the container, and it may only be dischargeable by manual removal, instead of the typical gravity method of tilting the container to a maximum of 45° to effectively pour the product out of the container.
Although, air fluidization is not the solution to all products' flow issues (for instance bulk commodities exhibiting bridging or tunneling do not respond to pneumatic fluidization), it is the most prevalent solution for most hard to flow bulk commodities, and even in those cases where the bulk commodity is not sensitive to pneumatic fluidization, it can be used in combination with other type of fluidization (shaking, vibrating, etc.) that renders or assists the pneumatic fluidization to be additively effective as well.
Many devices exist to aid in the fluidization of these products, outside of the container liner-bag, and typically they were applied at the discharge port or door side of the liner-bag. These devices included fluidizing lances, fluidizing, hoppers, de-compacting hoppers with built-in conveyors, industrial vibrators, shaking platforms, and very often even a combination of some of these devices into one for aiding in the fluidization of the product during unloading. However, a comprehensive and systemic solution to fluidization of these products, requires the creation of a fluidization bed inside of the container liner-bag as well for even transmission of the fluid throughout the container liner-bag, into these products in the container.
One of the most prevalent methods to create an airbed for fluidizing the product inside of the container liner-bag, consists of insetting on top of the floor panel of the liner-bag, a perforated plastic hose evenly distributed across the width and length of the liner-bag in an S-shaped pattern. The two ends of the hose are kept outside of the liner-bag, and pressurized air is injected through them to provide continuous air flow that escapes through the small perforations of the hose. As the air escapes through the minute holes into the container liner-bag interior, it creates (in theory) a continuous stream of aeration that as it trickles up through the product, it eventually achieves the desired fluidization of the bulk product in direct contact with these air jets and then through the rest of the bulk product.
Although this method in theory is effective at creating an airbed, its use in practice has numerous shortcomings. One such shortcoming is that as the product is removed from the container at the front end of the container, the air hose starts to become exposed on the front end of the container. As a growing percentage of the injected air just escapes from the exposed front end parts of the hose, the airbed increasingly loses its effectiveness; and the perforated hose across the floor of the container eventually becomes a barrier itself to the outflow of the product, as the container is tilted to 45′.
Because the air hose ends up becoming, a barrier to the product's outflow, the product starts dragging down on the liner and the perforated hose, which ends up jammed down on the back end of the container and the airbed is rendered almost useless. An attempted solution to this problem, has been to affix the perforated hose to the floor so as to prevent its movement, but in many instances this results in the liner floor of the container bag being torn by the effect of the product pulling down on the fixed hose which is attached to the liner floor.
The S-shaped air hoses are also often bent or pinched, and therefore rendered useless, when the container liner-bag is folded and unfolded, due to the nature of the packing process that requires the liner-bag and air hoses to be folded and unfolded together numerous times in their process of use.